Respiratory assistance apparatus

ABSTRACT

A respiratory assistance apparatus has a gases inlet configured to receive a supply of gases, a blower unit configured to generate a pressurised gases stream from the supply of gases; a humidification unit configured to heat and humidify the pressurised gases stream; and a gases outlet for the heated and humidified gases stream. A flow path for the gases stream extends through the respiratory device from the gases inlet through the blower unit and humidification unit to the gases outlet. A sensor assembly is provided in the flow path before the humidification unit. The sensor assembly has an ultrasound gas composition sensor system for sensing one or more gas concentrations within the gases stream.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to respiratory assistance apparatus that providesa stream of heated and humidified gases to a user for therapeuticpurposes. In particular, although not exclusively, the respiratoryassistance apparatus may provide respiratory assistance to patients orusers who require a supply of heated and humidified gases forrespiratory therapies such as respiratory humidification therapy,high-flow oxygen therapy, Positive Airway Pressure (PAP) therapies,including CPAP therapy, Bi-PAP therapy, and OPAP therapy, and typicallyfor the treatment of diseases such as Obstructive Sleep Apnea (OSA),snoring, or Chronic Obstructive Pulmonary Disease (COPD).

2. Description of the Related Art

Respiratory assistance devices or systems for providing a flow ofhumidified and heated gases to a patient for therapeutic purposes arewell known in the art. Systems for providing therapy of this type (forexample respiratory humidification) typically have a structure wheregases are delivered to a humidifier chamber from a gases source, such asa blower (also known as a compressor, an assisted breathing unit, a fanunit, a flow generator or a pressure generator). As the gases pass overthe hot water, or through the heated and humidified air in thehumidifier chamber, they become saturated with water vapour. The heatedand humidified gases are then delivered to a user or patient downstreamfrom the humidifier chamber, via a gases conduit and a user interface.

In one form, such respiratory assistance systems can be modular systemsthat comprise a humidifier unit and a blower unit that are separate(modular) items. The modules are connected in series via connectionconduits to allow gases to pass from the blower unit to the humidifierunit. For example, FIG. 1 shows a schematic view of a user 1 receiving astream of heated and humidified air from a modular respiratoryassistance system. Pressurised air is provided from an assistedbreathing unit or blower unit 2 a via a connector conduit 10 to ahumidifier chamber 4 a. The stream of humidified, heated and pressurisedair exits the humidification chamber 4 a via a user conduit 3, and isprovided to the patient or user 1 via a user interface 5.

In an alternative form, the respiratory assistance systems can beintegrated systems in which the blower unit and the humidifier unit arecontained within the same housing. A typical integrated system consistsof a main blower unit or assisted breathing unit which provides apressurised gases flow, and a humidifier unit that mates with or isotherwise rigidly connected to the blower unit. For example, thehumidifier unit is mated to the blower unit by slide-on or pushconnection, which ensures that the humidifier unit is rigidly connectedto and held firmly in place on the main blower unit. FIG. 2 shows aschematic view of the user 1 receiving heated and humidified air from anintegrated respiratory assistance system 6. The system operates in thesame manner as the modular system shown in FIG. 1, except thehumidification chamber 4 b has been integrated with the blower unit toform the integrated system 6.

The user interface 5 shown in FIGS. 1 and 2 is a nasal mask, coveringthe nose of the user 1. However, it should be noted that in systems ofthese types, a mask that covers the mouth and nose, a full face mask, anasal cannula, or any other suitable user interface could be substitutedfor the nasal mask shown. A mouth-only interface or oral mask could alsobe used. Also, the patient or user end of the conduit can be connectedto a tracheostomy fitting, or an endotracheal intubation.

U.S. Pat. No. 7,111,624 includes a detailed description of an integratedsystem. A ‘slide-on’ water chamber is connected to a blower unit in use.A variation of this design is a slide-on or clip-on design where thechamber is enclosed inside a portion of the integrated unit in use. Anexample of this type of design is shown in WO 2004/112873, whichdescribes a blower, or flow generator 50, and an associated humidifier150.

For these integrated systems, the most common mode of operation is asfollows: air is drawn by the blower through an inlet into the casingwhich surrounds and encloses at least the blower portion of the system.The blower pressurises the air stream from the flow generator outlet andpasses this into the humidifier chamber. The air stream is heated andhumidified in the humidifier chamber, and exits the humidifier chambervia an outlet. A flexible hose or conduit is connected either directlyor indirectly to the humidifier outlet, and the heated, humidified gasesare passed to a user via the conduit. This is shown schematically inFIG. 2.

In both modular and integrated systems, the gases provided by the blowerunit are generally sourced from the surrounding atmosphere. However,some forms of these systems may be configured to allow a supplementarygas to be blended with the atmospheric air for particular therapies. Insuch systems, a gases conduit supplying the supplemental gas istypically either connected directly to the humidifier chamber orelsewhere on the high pressure (flow outlet) side of the blower unit, oralternatively to the inlet side of the blower unit as described in WO2007/004898. This type of respiratory assistance system is generallyused where a patient or user requires oxygen therapy, with the oxygenbeing supplied from a central gases source. The oxygen from the gasessource is blended with the atmospheric air to increase the oxygenfraction before delivery to the patient. Such systems enable oxygentherapy to be combined with high flow humidification therapy for thetreatment of diseases such as COPD. In such therapies, it is importantthat the oxygen fraction being delivered to the patient be known andcontrolled. Currently, the oxygen fraction being delivered to thepatient is typically manually calculated or estimated based on a printedlook-up table that sets out various oxygen fractions that have beenpre-calculated based on a range of oxygen flow rates supplied from thecentral gas source and a range of flow rates generated by the blowerunit.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

It is an object of the present invention to provide a respiratoryassistance apparatus with an improved gas composition sensingcapability, or to at least provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect, the present invention broadly consists in arespiratory assistance apparatus configured to provide a heated andhumidified gases stream, comprising: a gases inlet configured to receivea supply of gases; a blower unit configured to generate a pressurisedgases stream from the supply of gases; a humidification unit configuredto heat and humidify the pressurised gases stream; a gases outlet forthe heated and humidified gases stream; a flow path for the gases streamthrough the respiratory device from the gases inlet through the blowerunit and humidification unit to the gases outlet; a sensor assemblyprovided in the flow path before the humidification unit, the sensorassembly comprising an ultrasound gas composition sensor system forsensing one or more gas concentrations within the gases stream.

Preferably, the ultrasound gas composition sensor system may comprise atransmitter and receiver transducer pair that may be operable totransmit cross-flow acoustic pulses from the transmitter to the receiverthrough the gases stream for sensing the speed of sound in the gasesstream in the vicinity of the sensor assembly.

In one form, the transmitter and receiver transducer pair may bearranged such that the acoustic pulses traverse the gases stream in across-flow that is in a direction substantially perpendicular to theflow direction of the gases stream.

In another form, the transmitter and receiver transducer pair may bearranged such that the acoustic pulses traverse the gases stream in across-flow that is angled but not perpendicular with respect to the flowdirection of the gases stream.

In one form, the transmitter and receiver transducer pair may comprise atransducer that is configured as a transmitter and a transducer that isconfigured as a receiver for transmitting uni-directional acousticpulses.

In another form, the transmitter and receiver transducer pair maycomprise a pair of transmitter-receiver transducers that are configuredfor transmitting bi-directional acoustic pulses.

In one form, the transmitter and receiver may be aligned with each otherin relation to the flow direction of the gases stream and facing eachother on opposite sides of the flow path.

In another form, the transmitter and receiver may be displaced from eachother in the flow direction of the gases stream.

Preferably, the acoustic pulses may have a beam path that is directbetween the transmitter and receiver. Alternatively, the acoustic pulsesmay have a beam path that is indirect between the transmitter andreceiver and which undergoes one or more reflections.

In another form, the transmitter and receiver transducer pair may be inthe form of a single transmitter-receiver that is configured to transmitcross-flow acoustic pulses and receive the echo return pulses.

In another form, the ultrasound gas composition sensor system maycomprise a transmitter and receiver transducer pair that are operable totransmit along-flow acoustic pulses from the transmitter to the receiverthrough the gases stream for sensing the speed of sound in the gasesstream in the vicinity of the sensor assembly.

Preferably, the respiratory assistance apparatus may further comprise asensor control system that is operatively connected to the transmitterand receiver transducer pair of the ultrasound gas composition sensorsystem and which is configured to operate the transducer pair to senseand generate a speed of sound signal indicative of the speed of soundthrough the gases stream.

Preferably, the sensor control system is configured to generate one ormore gas concentration signals indicative of the gas concentrationwithin the gases stream based at least on the signal indicative of thespeed of sound though the gases stream.

In one form, the sensor assembly may further comprise a temperaturesensor that is configured to measure the temperature of the gases streamin the vicinity of the sensor assembly and generate a representativetemperature signal, and wherein the sensor control system is configuredto generate one or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of soundsignal, and the temperature signal.

In another form, the sensor assembly may further comprise a humiditysensor that is configured to measure the humidity of the gases stream inthe vicinity of the sensor assembly and generate a representativehumidity signal, and wherein the sensor control system is configured togenerate one or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of soundsignal, and the humidity signal. By way of example, the humidity sensormay be a relative humidity sensor or an absolute humidity sensor.

In another form, the sensor assembly may comprise both a temperaturesensor and a humidity sensor for measuring the temperature and humidityof the gases stream in the vicinity of the sensor assembly andgenerating respective representative temperature and humidity signals,and wherein the sensor control system is configured to generate one ormore gas concentration signals indicative of the gas concentrationwithin the gases stream based on the speed of sound signal, temperaturesignal, and humidity signal.

Preferably, the sensor control system may be configured to apply atemperature correction to the temperature signal to compensate for anypredicted temperature sensing error created by heat within therespiratory device that affects the temperature sensor.

Preferably, the sensor assembly may further comprise a flow rate sensorthat is configured to sense the flow rate of the gases stream in thevicinity of the sensor assembly and generate a representative flow ratesignal; and the system may further comprise: a motor speed sensor beingprovided that is configured to sense the motor speed of the blower unitand generate a representative motor speed signal, and wherein thetemperature correction is calculated by the sensor control system basedat least on the flow rate signal and/or motor speed signal.

In one form, the sensor control system may be configured to generate agas concentration signal representing the oxygen concentration in thegases stream.

In another form, the sensor control system may be configured to generatea gas concentration signal representing the carbon dioxide concentrationin the gases stream.

Preferably, the sensor assembly may be releasably mounted within theflow path.

Preferably, the flow path may be shaped or configured to promote stableflow of the gases stream in at least one section or portion of the flowpath.

Preferably, the flow path may be shaped or configured to promote stableflow in a section or portion of the flow path containing the sensorassembly.

Preferably, the flow path may comprise one or more flow directors at ortoward the gases inlet. More preferably, each flow director may be inthe form of an arcuate fin.

In one form, the flow path may comprise at least one spiral portion orsection to promote stable flow of the gases stream. Preferably, the flowpath may comprise an inlet section that extends between the gases inletand the blower unit and the inlet section comprises at least one spiralportion.

Preferably, the sensor assembly may be located in a spiral portion ofthe flow path. More preferably, the spiral portion comprises one or moresubstantially straight sections, and the sensor assembly is located inone of the straight sections.

Preferably, the sensor assembly may comprise a sensor housing comprisinga main body that is hollow and defined by peripheral walls that extendbetween a first open end and a second open end to thereby define asensing passage in the main body between the walls through which thegases stream may flow in the direction of a flow axis extending betweenthe first and second ends of the main body, and wherein the transmitterand receiver transducer pair are located on opposite walls or sides ofthe sensing passage. More preferably, the sensor housing may comprise: amain body comprising two spaced-apart side walls, upper and lower wallsextending between the side walls to define the sensing passage along themain body between its first and second ends; and a pair of transducermounting assemblies located on opposing walls of the main body, whichare each configured to receive and retain a respective transducer of thetransducer pair such that they are aligned, and face each other, acrossthe sensing passage of the main body.

Preferably, the blower unit may be operable to generate a gases streamat the gases outlet having a flow rate of up to 100 litres-per-minute.

In one form, the gases inlet may be configured to receive a supply ofgases comprising a mixture of atmospheric air and pure oxygen from anoxygen supply. In another form, the gases inlet may be configured toreceive a supply of gases comprising a mixture of atmospheric air andcarbon dioxide from a carbon dioxide supply.

Preferably, the flow path is in the bulk flow path of the apparatus.

In a second aspect, the present invention broadly consists in a sensorassembly for in-line flow path sensing of a gases stream in arespiratory assistance apparatus comprising: a sensor housing comprisinga main body that is hollow and defined by peripheral walls that extendbetween a first open end and a second open end, to thereby define asensing passage in the main body between the walls, through which thegases stream may flow in the direction of a flow axis extending betweenthe first and second ends of the main body; an ultrasound gascomposition sensor system mounted in the sensor housing for sensing oneor more gas concentrations within the gases stream flowing in thesensing passage; a temperature sensor mounted in the sensor housing forsensing the temperature of the gases stream flowing in the sensingpassage; and a flow rate sensor mounted in the sensor housing forsensing the flow rate of the gases stream flowing in the sendingpassage.

Preferably, the sensor housing may be configured for releasableengagement into a complementary retaining aperture in the flow path ofthe respiratory assistance apparatus.

Preferably, the ultrasound gas composition sensor system may comprise atransmitter and receiver transducer pair that are operable to transmitacoustic pulses from the transmitter to the receiver through the gasesstream in a direction substantially perpendicular to the flow axis ofthe gases stream flowing through the sensing passage.

Preferably, the transmitter and receiver transducer pair may be locatedon opposite walls or sides of the sensing passage.

Preferably, the main body of the sensor housing may comprise twospaced-apart side walls, and upper and lower walls that extend betweenthe side walls to define the sensing passage along the main body betweenits first and second ends; and a pair of transducer mounting assemblieslocated on opposing walls of the main body, which are each configured toreceive and retain a respective transducer of the transducer pair suchthat they are aligned, and face each other, across the sensing passageof the main body.

Preferably, the pair of transducer mounting assemblies may be located onopposite side walls of the main body, and wherein each transducermounting assembly comprises a retaining cavity within which a respectivetransducer of the pair are received and retained.

Preferably, each transducer mounting assembly may comprise a cylindricalbase portion that extends from a respective side wall of the main bodyand at least one pair of opposed clips that extend from the baseportion, the base portion and clips collectively defining the retainingcavity.

Preferably, each side wall of the main body may comprise a transduceraperture which is co-aligned with its associated transducer mountingassembly and through which the front operating face of the transducermay extend to access the sensing passage.

Preferably, the transducer mounting assemblies may be configured tolocate their respective transducers such that the operating faces of thetransducers are substantially flush with the inner surface of theirrespective wall of the main body of the sensor housing.

The second aspect of the invention may have any one or more of thefeatures mentioned in respect of the sensor assembly of the first aspectof the invention.

The phrase “stable flow” as used in this specification and claims means,unless the context suggests otherwise, a type of gases stream flow,whether laminar or turbulent, that promotes or causes the properties orcharacteristics of the flow being measured or sensed to be substantiallytime-invariant for a given set of conditions at the scale the propertiesor characteristics are being measured or sensed.

The phrases “cross-flow beam” or “cross-flow” as used in thisspecification and claims mean, unless the context suggests otherwise, anultrasound pulse or beam that is transmitted in a beam path across ortransversely to the main gases flow path direction or axis as opposed toalong the main gases flow path direction. For example, a cross-flow beammay be transmitted across the gases flow path in a directionsubstantially perpendicular to the main gases flow path direction oraxis, although other cross-flow angles are intended to be covered by theterm also.

The phrases “along-flow beam” or “along-flow” as used in thisspecification and claims mean, unless the context suggests otherwise, anultrasound pulse or beam that is transmitted in a beam path that issubstantially aligned, whether parallel or coincident, with the maingases flow path direction or axis, whether transmitted in a directionthat is with or against the gases flow direction.

The term “comprising” as used in this specification and claims means“consisting at least in part of”. When interpreting each statement inthis specification and claims that includes the term “comprising”,features other than that or those prefaced by the term may also bepresent. Related terms such as “comprise” and “comprises” are to beinterpreted in the same manner.

Number Ranges

It is intended that reference to a range of numbers disclosed herein(for example, 1 to 10) also incorporates reference to all rationalnumbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5,7, 8, 9 and 10) and also any range of rational numbers within that range(for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, allsub-ranges of all ranges expressly disclosed herein are hereby expresslydisclosed. These are only examples of what is specifically intended andall possible combinations of numerical values between the lowest valueand the highest value enumerated are to be considered to be expresslystated in this application in a similar manner.

As used herein the term “and/or” means “and” or “or”, or both.

As used herein “(s)” following a noun means the plural and/or singularforms of the noun.

The invention consists in the foregoing and also envisages constructionsof which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described by way ofexample only and with reference to the drawings, in which:

FIG. 1 is a schematic view of a known form of respiratory assistanceapparatus having a modular configuration blower unit connected to ahumidifier unit;

FIG. 2 is a schematic view of another known form of respiratoryassistance apparatus in which the blower unit and humidifier unit areintegrated into a single main housing;

FIG. 3 shows a perspective view of the main housing of a respiratoryassistance apparatus in accordance with an embodiment of the invention;

FIG. 4 shows a side elevation view of the respiratory assistanceapparatus of FIG. 3;

FIG. 5 shows a front elevation view of the respiratory assistanceapparatus from direction A in FIG. 4;

FIG. 6 shows a rear elevation view of the respiratory assistanceapparatus from direction B of FIG. 4;

FIG. 7 shows an underside view of the respiratory assistance apparatusof FIG. 3;

FIG. 8 shows a plan view of the respiratory assistance apparatus of FIG.3;

FIG. 9 shows a perspective view of the respiratory assistance apparatusof FIG. 3 with an upper part of the main housing removed and exposingthe electronic control circuitry and blower unit compartment;

FIG. 10 shows a perspective view of the respiratory assistance apparatusof FIG. 9 with the electronic control circuitry, outer blower unitcasing, and other components removed exposing the upper side of theinner blower casing for the motor and impeller;

FIG. 10A shows a perspective view of the respiratory assistanceapparatus of FIG. 3 with a lower part of the main housing and basecompartment removed and exposing the underside of the main outer blowerunit casing and inner blower casing;

FIG. 11 shows a perspective view of the respiratory assistance apparatusof FIG. 10 with the inner blower casing and humidification chamber inletconnector removed exposing the upper side of the main housing basecompartment;

FIG. 12 shows a perspective view of the respiratory assistance apparatusof FIG. 11 with the lower part of the main housing removed exposing thebase compartment and humidifier unit compartment;

FIG. 13 shows a plan view of the respiratory assistance apparatus ofFIG. 12;

FIG. 14 shows a rear end elevation view of the respiratory assistanceapparatus of FIG. 12 from direction C;

FIG. 15 shows an underside view of the respiratory assistance apparatusof FIG. 12 and showing a sensor assembly and a first embodiment of aninlet section of the gases stream flow path having a spiral flow path;

FIG. 16 shows a perspective view of the underside of the respiratoryassistance apparatus of FIG. 12;

FIG. 17 shows a close-up perspective view of the underside of therespiratory assistance apparatus of FIG. 12 and in particular a portionof the inlet section of the gases stream flow path and sensor assembly;

FIG. 18A shows an underside view of the respiratory apparatus of FIG.12, showing a sensor assembly and a second embodiment of an inletsection of the gases stream flow path having a direct flow path;

FIG. 18B shows a rear end elevation view of the respiratory assistanceapparatus of FIG. 18A with the direct inlet flow path;

FIG. 18C shows a perspective view of the underside of the respiratoryapparatus of FIG. 18A;

FIG. 19 shows a perspective view of a housing of a sensor assembly inaccordance with an embodiment of the invention;

FIG. 20 shows a perspective view of the sensor assembly housing of FIG.19 with an arrangement of sensors mounted to the housing;

FIG. 21 shows an underside view of the housing of the sensor assembly ofFIG. 19;

FIG. 22 shows a plan view of the top side of the housing of the sensorassembly of FIG. 19;

FIG. 23 shows a side elevation view of the housing of the sensorassembly of FIG. 19;

FIG. 24 shows an end elevation view of the housing of the sensorassembly of FIG. 19;

FIG. 25 shows a block diagram of a sensor control system of therespiratory assistance apparatus in accordance with an embodiment of theinvention;

FIGS. 26A-26E show schematic diagrams of various ultrasonic transducerconfigurations for the sensor assembly using cross-flow beams; and

FIGS. 27A-27C show schematic diagrams of various ultrasonic transducerconfigurations for the sensor assembly using along-flow beams.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Overview

This invention relates primarily to a sensor assembly and associatedsensor control circuitry for sensing various characteristics of a streamof gases flowing in a respiratory assistance apparatus. By way ofexample, an embodiment of the sensor assembly and sensor control systemwill be described with reference to a respiratory assistance apparatusof the integrated system type in which the blower unit is integratedwith the humidification unit in a single housing. However, it will beappreciated that the sensor assembly and associated sensor controlsystem may be implemented in a modular type respiratory assistanceapparatus system in which the humidification unit is separate from theblower unit.

Further, the embodiment to be described is with reference to arespiratory assistance apparatus being used particularly for high-flowhumidification and oxygen therapy in which the stream of gases can beconsidered a binary gas mixture of atmospheric air blended withsupplementary oxygen (O2) such that the oxygen fraction of the stream ofgases delivered to the end user has an increased oxygen fractionrelative to atmospheric air. In the art, supplementing or blending theatmospheric gases with another gas is known as ‘augmentation’ and istypically used to vary the concentration of a particular gas, such asoxygen or nitrogen, relative to its concentration in atmospheric air.

It will be appreciated that the sensor assembly and sensing circuitrymay alternatively be implemented in other respiratory assistanceapparatuses that are particularly configured for or controlled for usein other respiratory therapies, such as PAP therapies, whether suchsystems deliver a stream of pressurised gases of atmospheric air only oratmospheric air augmented with another particular gas, such as oxygen ornitrogen. It will be appreciated that while the sensor assembly andsensor control system are primarily configured for sensing the oxygenfraction of a binary gases mixture comprising atmospheric gasesaugmented with oxygen, the sensor assembly and sensor control system mayalso be configured or adapted to sense characteristics of a gases streamwhich comprise other augmented air blends or binary gas mixtures, suchas atmospheric air augmented with nitrogen (N2) from a nitrogen supplyor augmented with carbon dioxide (CO2) from a carbon dioxide supply orany other suitable supplemental gas, or helium augmented with oxygen orany other suitable binary gas mixtures.

Integrated Respiratory Assistance Apparatus for High-Flow Humidificationand Oxygen Therapy

Referring to FIG. 3, the main housing of the integrated respiratoryassistance apparatus 10 (respiratory device) in accordance with anembodiment of the invention is shown. The respiratory device 10comprises a blower unit that generates a stream of pressurised orhigh-flow gases which is then heated and humidified by a humidificationunit in a manner previously described. Although not shown in FIG. 3, thegases stream generated by the respiratory device 10 is typicallydelivered to a patient by a patient interface that typically comprises aflexible delivery conduit or tube that is connected at one end to agases outlet 12 of the respiratory device 10, and at the other end, to auser interface, which is typically a nasal cannula, or alternatively maybe a nasal mask, full face mask, tracheostomy fitting, or any othersuitable user interface.

In this embodiment, the respiratory device 10 is provided with ahumidification unit 15 of the type previously described with referenceto FIG. 2 for example. The humidification unit 15 comprises ahumidification water chamber 17 and heater plate 19 which are installedwithin a humidification unit compartment generally indicated at 14located at or toward the front end 11 of the main housing. Referring toFIGS. 3 and 5, the humidification chamber 17 is provided with an inletport 16 and outlet port 18 for connecting the chamber into the flow pathof the respiratory device when installed. For example, the inlet port 16is connected into the flow path after the blower unit such that thehumidification chamber 17 receives a stream of pressurised or high-flowgases through the inlet from the blower unit located at or toward therear end 13 of the main housing. Once heated and humidified, the streamof gases exits the humidification chamber via its outlet port 18, whichis fluidly connected to the gases outlet 12 of the respiratory device10.

Referring to FIG. 6, a gases inlet assembly 20 of the respiratory device10 is shown at the rear end 13 of the main housing. In this embodiment,the gases inlet assembly 20 comprises one or more atmospheric air inletvents 22 through which ambient atmospheric air is drawn into the deviceby the blower unit and a supplemental gas connection inlet 24 which maybe connected to a central gases supply of a supplemental gas, such as aflow of oxygen for blending with the atmospheric air to increase theoxygen fraction. As will be explained in further detail later, thebinary gas mixture of air and oxygen is drawn or sucked in by the blowerunit and pressurised into a gas stream of a desired flow rate forsubsequent delivery into the humidification unit where it is heated andhumidified before delivery to the end user via a patient interface tocomplete the breathing circuit.

Reverting to FIG. 3, in this embodiment the main housing of therespiratory device 10 is of a two-part construction comprising a lowerhousing part 26 that is releasably coupled or fitted to an upper housingpart 28 and which when assembled together form the overall main housingor casing which encloses the blower unit and provides the humidificationunit compartment for receiving the humidification chamber. However, itwill be appreciated that a multi-part housing construction of more thantwo parts or a single integral main housing may alternatively beemployed. In this embodiment, the housing parts are moulded fromplastic, but it will be appreciated that one or more components or partsof the housing may be formed from other materials if desired.

Referring to FIG. 7, the main base or underside portion 26 a of thelower housing part 26 is shown. Referring to FIG. 8, a user controlinterface 30 is provided on the main upper portion 28 a of the upperhousing part 28 and which may comprise user controls and/or a userdisplay for controlling the respiratory device 10.

Referring to FIG. 9, the respiratory device 10 is shown with the upperhousing part 28 removed and exposing the main or outer blower unitcasing 32 of the blower unit compartment that in this embodiment ishoused and located toward the rear end 13 of the main housing. A printedcircuit board 31 comprising the control system electronics of therespiratory device 10 and being mounted alongside the blower unit casing32 is also visible in FIG. 9. Also more clearly shown are the connectorsand/or conduits 23,25 which fluidly connect the inlet 16 and outlet 18ports of the humidification chamber 17 to the blower unit and gasesoutlet 12, respectively. FIG. 10 shows the inner blower casing 34 whichhouses the motor and impeller of the blower unit. The gases outlet ofthe blower unit is indicated generally at 35. The inner blower casing 34is mounted or housed inside the main blower unit casing 32 shown in FIG.9.

Referring to FIG. 10A, the gases outlet 35 of the blower unit can beseen more clearly. The blower unit is also provided with a central gasesinlet aperture or port 37 through which gases are drawn by the rotatingimpeller of the blower unit. In this embodiment, the inlet port 37 ofthe blower unit is fluidly connected by a flow path to the gases inletassembly 20.

Referring to FIG. 11, a base compartment 36 is situated beneath theblower unit at or toward the rear end 13 of the main housing. In thisembodiment, the base compartment 36 is mounted to or within the lowerhousing part 26. The base compartment 36 comprises an exit port oraperture 38 in its upper portion or lid 36 a that is fluidly connectedby conduit and/or connectors to the inlet port 37 of the blower unitsuch that in operation the gases stream flows through into the blowerunit from the base compartment 36 after entering the gases inletassembly 20. FIG. 12 shows the base compartment 36 more clearly with thelower housing part 26 of the main housing omitted from view. Thehumidification unit compartment 14 is also more clearly visible in FIG.12.

Flow Path of Gases Stream

In operation, the flow or stream of gases is transported from the gasesinlet assembly 20 to the gases outlet 12 via a flow path through therespiratory device 10. In this embodiment, the flow path starts at thegases inlet assembly 20 where the stream of gases, such as atmosphericair blended with supplemental oxygen enter the respiratory device 10 andare channeled or transported through an inlet section of the flow pathin the base compartment 36 prior to entering the blower unit compartmentabove. Upon exiting the inlet section of the flow path, the stream ofgases enters the blower unit where the gases are pressurised oraccelerated into a high flow gas stream having a controllable flow rate,which is typically high flow for high-flow humidification therapies. Insuch applications, the flow rate may range from about 1 L/min to about100 L/min, and more preferably from about 2 L/min to about 60 L/min. Theflow path exits the blower unit and enters the fluidly connected (e.g.via conduits and/or connectors and/or ports) humidification unit inwhich the gases stream is heated and humidified. The flow pathterminates with the gases stream being transported from the outlet 18 ofthe humidification unit to the gases outlet 12 of the respiratory device10.

It will be appreciated that certain portions or sections of the flowpath of the gases stream may be fully sealed, for example the flow pathafter the humidification unit. Additionally, the flow path may also besealed between the humidification unit and blower unit, and the inletsection of the flow path prior to the blower unit may also optionally besubstantially sealed along a significant portion after the gases inletassembly 20. It will be appreciated that the flow path for transportingthe gases stream may be defined by conduits, ports and/or connectorsfluidly connecting various components, such as the blower unit to thehumidification unit, and/or generally by the formation of the housingand casings within the respiratory device which can be configured withenclosed channels or passages, for example formed from internal walls orsurfaces, for directing the gases stream through the respiratory device.

Spiral Inlet Flow Path First Embodiment

FIG. 14 shows the inlet aperture 58 formed in the rear of the basecompartment 36. The inlet aperture 58 is situated behind gases inletassembly 20. Referring to FIG. 15, a first embodiment of the inletsection of the gases stream flow path will be described. The inletsection of the gases stream flow path is provided in the basecompartment 36 of the main housing and extends from the gases inletassembly 20 at the rear of the respiratory device 10 to the exit port 38of the base compartment, prior to entering the inlet port 37 of theblower unit above. As shown in FIG. 15, the inlet section of the flowpath as shown generally follows the path shown by arrows XX.

In this embodiment, at least a portion of the inlet section of the flowpath is shaped or configured to promote stable air flow upon reachingthe exit port 38, and before entering the blower unit compartment viathe exit port 38. The stable air flow assists to reduce noise andincreases the accuracy of the sensed gas characteristics measured by thesensor assembly in the sensor zone of the flow path. In this embodiment,the stable flow is created or provided by at least a portion of theinlet section of the flow path being spiraled or providing a spiraledcourse or path. For example, as shown in FIG. 15, at least a portion ofthe flow path indicated by arrows XX is in the form of a graduallytightening path. The phrases “spiraled” or “spiral” are intended to meanany form of flow path that is continuous and gradually winds in uponitself from a start point to an end point, with one or multiple turns.It is intended to cover any uniform or non-uniform spiral path, whethera continuous and gradually tightening curve of reducing radius relativeto a central point or axis wherein the rate of reducing radius may beconstant or varied, or an arbitrarily shaped spiral path as shown inFIG. 14 wherein the flow path winds in upon itself (i.e. with at leastone turn) such that the path spirals towards a reference point locatedwithin the outer most turn, whether the reference point is locatedcentrally or not.

The spiral portion of the flow path may form a substantial part of theentire inlet section of the flow path, or alternatively, may form aminor part of the inlet section of the flow path depending on designrequirements. In this embodiment, the spiral portion of the flow pathstarts at about where indicated at 42 and ends after just over oneinward spiral turn at about where indicated at 44. The inlet section ofthe flow path starts at an inlet zone with an initial section or portiongenerally indicated at 46 prior to the start 42 of the spiral portion,and then finishes at a terminating section or portion generallyindicated at 48 after the end 44 of the spiral portion. In thisembodiment, the terminating portion of the inlet section of the flowpath is in the form of a gradually widening flow path that opens into alarger transition zone 48 within which the exit port 38 to the blowerunit is located. The transition zone 48 comprises a substantially curvedperimeter wall that may substantially conform to at least a portion ofthe circumference of a circle, or which is otherwise curved or concavein shape when viewed in plan. In FIG. 15, the circumferential perimeterwall section of the transition zone is defined between 50 and 52 aboutcentre point Y in the transition zone 48. The shape of the wall in thetransition zone is configured to continue to promote stable flow of thegases stream as it exits the inlet section of the flow path and into theblower unit.

As previously described, the flow path within the respiratory device 10may be formed from a combination of conduit or tubing or the housing orcasings of the respiratory device including connectors, ports and/orother couplings that fluidly connect the various sections of the flowpath. In this embodiment, the inlet section of the flow path issubstantially defined by two co-extending walls 54 and 56 that arespaced-apart from each other and which are enclosed within the basecompartment to form an enclosed conduit, channel or passageway byhorizontally extending upper and lower walls or surface, such as theupper lid 36 a of the base compartment and the base or underside portion26 a of the lower housing part 26 of the main housing (see FIG. 7). Asshown in this embodiment, the walls 54, 56 are upright and extendsubstantially perpendicularly or vertically relative to thesubstantially horizontal enclosing upper lid 36 a of the basecompartment and underside portion 26 a of the lower housing part 26. Itwill be appreciated that the flow path defined by the co-extending walls54 and 56 may alternatively be enclosed from above and/or below by oneor more planar plates or members. In this embodiment, the flow path, atleast within the spiral portion of the inlet section, has asubstantially rectangular or square cross-sectional shape, although itwould be appreciated that this is not essential. In alternativeembodiments, the flow path may be configured to have any other desiredcross-sectional shape, including circular, oval, or otherwise, and theshape may be uniform along the length of the flow path or may varybetween two or more shapes and/or sizes. It will also be appreciatedthat the inlet section and particularly the spiral portion of the inletsection of the flow path may be formed from a rigidly shaped conduit ortubing that is formed to extend in the desired spiral shape.

The cross-sectional area of the spiral portion of the inlet section ofthe flow path in this embodiment is substantially uniform along thelength of the spiral portion, although in alternative embodiments thecross-sectional area may be non-uniform along the length of the spiralportion. In particular, the width (W) between the co-extending walls 54and 56, is substantially constant throughout the spiral portion of theinlet section in this embodiment, but may be varied along the length ofthe spiral portion in alternative embodiments if desired. With referenceto FIG. 17, the height (H) of the walls is also preferably constantalong at least the spiral portion of the inlet section of the flow path,but may be configured to vary in other embodiments if desired.

In this embodiment, the entire inlet section of the flow path extendssubstantially within the same plane within the base compartment 36 suchthat there is no vertical deviation or displacement of the flow pathwithin the inlet section, and at least within the spiral portion of theinlet section, until the flow path transitions to the exit port 38 whereit extends vertically up into the blower unit casing 32 above the basecompartment 36.

In this embodiment, there is a single spiral portion locatedsubstantially prior to the transition zone of the flow path where itenters the blower unit compartment 32. However, in alternativeembodiments, it will be appreciated that the flow path may comprise twoor more separate spiral portions located in series in the flow path. Ifthere are a plurality of spiral portions, they may all be located priorto the blower unit or in the flow path after the blower unit prior tothe humidifier unit, or alternatively, at least one spiral portion ineach region may be provided. In the preferred embodiment, the spiralportion or portions are provided preferably before the flow path entersthe humidification unit, and more preferably, prior to the flow pathentering the blower unit, or any other section of the flow path in whichstable flow promotion is beneficial for noise reduction or gases streamcharacteristics sensing accuracy.

Sensor Assembly

Referring to FIGS. 15-17, the respiratory device 10 comprises a sensorassembly 60 located or situated in-line with the flow path prior to thehumidification unit for sensing various characteristics or parameters ofthe gases stream. In this embodiment, the sensor assembly 60 is providedin a sensor zone of the inlet section of the flow path, and preferablywithin the spiral portion of the inlet section of the flow path when thegases stream has stable flow characteristics. The sensor assembly 60comprises a sensor housing as shown in FIGS. 16 and 17 that isconfigured or arranged to receive and retain one or more sensors orsensor components or sensor arrangements for detecting or sensing one ormore characteristics of the stream of gases flowing in the flow path.FIGS. 16 and 17 show the housing of the sensor assembly 60 without anysensors for clarity. The housing and sensors will be explained infurther detail with references to FIGS. 19-24.

In this embodiment, the sensor housing is a modular component that isreleasably secured, mounted, engaged, retained or fitted within the flowpath so that it may be removed if desired for replacement, maintenanceor repair. In this embodiment, the walls 56 and 54 of the flow path inthe inlet section are discontinuous within a substantially straightsection 61 of the flow path to thereby provide a receiving or mountingslot, aperture, recess or gap within which the sensor housing of thesensor assembly 60 may be received and retained. When installed, thehousing of the sensor assembly bridges the retaining gap provided by thediscontinuous walls 54, 56 so as to complete the flow path. With thisconfiguration, the sensor assembly 60 is configured to provide sensingof one or more characteristic of the flow of gases in the bulk flow orprimary flow path of the respiratory device. In other words, the sensorassembly 60 is not located in a separate chamber or secondary flow pathrelative to the bulk or primary flow path through the respiratorydevice.

In this embodiment, the sensor housing is configured to be received andretained within the mounting aperture of the flow path via a frictionfit. However, it will be appreciated that any other releasable mountingconfiguration or retention system may alternatively be used, including aclipping system, latching system, snap-fit, or any other releasableconfiguration.

The sensor assembly 60 may be configured or adapted to mount one or moresensors for sensing one or more characteristics of the flow of gases inthe flow path. Any suitable sensor may be mounted to the sensor housingas will be appreciated. In this embodiment, the sensor assembly at leastcomprises a gas composition sensor for sensing or measuring the gascomposition or concentration of one or more gases within the gasesstream. In this embodiment, the gas composition sensor is in the form ofan ultrasound gas composition sensor system that employs ultrasonic oracoustic waves for determining gas concentrations. In particular, theultrasound gas composition sensor utilizes binary gas sensing oranalysis for determining the relative gas concentrations of two gases ina binary gas mixture. In this embodiment, the gas composition sensor isconfigured to measure the oxygen fraction in the bulk gases stream flow,which consists of atmospheric air augmented with supplemental oxygen,which is essentially a binary gas mixture of nitrogen (N2) and oxygen(O2). It will also be appreciated that the ultrasonic gas concentrationsensor may be configured to measure the gas concentrations of otheraugmentation gases that have blended with atmospheric air in the gasesstream, including nitrogen (N2) and carbon dioxide (CO2), or any otherratio of two gases. For example, the ultrasonic gas concentration sensormay be configured to measure carbon dioxide (CO2) and deliver controlledcarbon dioxide levels to the patient to control the patient's breathingpattern. By adjusting the carbon dioxide levels to the patient, theCheyne-Stokes respiration of the patient can be controlled. Controllingthe patient's breathing pattern can be useful in some situations, suchas for athlete training to mimic high altitude conditions.

As previously described, in this embodiment, the respiratory device 10comprises a gases inlet assembly 20 that is configured to receiveambient atmospheric air and a supplementary gas, such as oxygen from anoxygen supply line or gas bottle. However, it will be appreciated thatthe air supply need not necessarily be ambient and the air may besupplied to the gases inlet assembly from an air supply line or gasbottle. Further, it will be appreciated that the respiratory device 10need not necessarily receive a supply of air. The respiratory device 10may be configured to receive a supply of any two or more suitable gasesfor blending and subsequent delivery to the end user via a patientinterface. The gases may be supplied to the gases inlet assembly of therespiratory device by any suitable means, including from central gasessupply lines, gas bottles, or otherwise.

In this embodiment, the sensor assembly 60 also comprises a temperaturesensor that is configured to measure the temperature of the gases streamand a flow rate sensor that is configured to sense the flow rate of thegases stream in the flow path.

Direct Inlet Flow Path Second Embodiment

Referring to FIGS. 18A-18C, a second embodiment of the inlet section ofthe gases stream flow path in the base compartment 36 will be described.Like reference numerals in the drawings represent like components withrespect to the first embodiment spiral inlet flow path described withreferences to FIGS. 14-17. In this second embodiment, the inlet sectionof the flow path is a shorter and more direct flow path between theinlet aperture 58 and exit port 38 of the base compartment 36. Theshorter and more direct flow path reduces gas residence time in the basecompartment, which reduces gas heat-up caused by the surroundingelectronic components.

In this embodiment, the inlet flow path can be defined by three mainzones or regions extending between the inlet aperture 58 and exit port38. The three regions are an inlet zone 39, a sensor zone 41, and atransition zone 43.

Referring to FIG. 18A, the inlet zone or region 39 extends between theinlet aperture 58 and approximately the transition line EE prior to thesensor zone 41. In this embodiment the inlet zone 39 of the inlet flowpath is defined between two walls 45, 47 which extend from at or towardthe inlet aperture 58 and through to the sensor assembly 60. In thisembodiment, the cross-sectional area of the inlet zone 39 graduallydiminishes or reduces from the inlet aperture 58 toward the transitionline EE into the sensor zone 41, such that the profile of the walls inthe inlet zone forms a funnel-like configuration. For example, the sidewalls 45 and 47 have a wider displacement from each other at the inletaperture 58 relative to their displacement from each other at or towardthe transition line EE. In other words, this distance or displacementbetween the side walls 45,47 reduces from the inlet aperture 58 to thetransition line EE such that the inlet zone 39 starts with a wideopening at the inlet aperture 58 and the flow path narrows progressivelytoward the transition line EE prior to the sensor zone 41. Thisfunnel-like configuration of the inlet zone creates an acceleratinggases stream flow, which promotes a more stable gas flow in thesubsequent sensor zone.

Optionally, the inlet zone 39 may be provided with one or more flowdirectors 49. In this embodiment, the inlet zone 39 comprises a bend inthat it is not a straight flow path directly from gases inlet assemblyto the sensor zone, and this may generate an uneven flow or velocitygradient across the inlet flow path in one or more regions of the inletflow path. To counteract this, the inlet zone 39 is provided with aplurality of flow directors 49 that are in the form of arcuate or curvedfins (more clearly seen in FIG. 18C) which are configured or providedwith a profile or shape that assists in promoting an even air flow intothe sensor zone 41 that is not biased toward any particular wall of theflow path. It will be appreciated that the number and shape or profileof the flow directors 49 may be varied to assist in directing the airflow at the desired angle into the sensor zone 41, but preferably thebulk flow is configured to enter the sensor zone at a substantiallyperpendicular direction relative to the transition line EE or frontopening of the sensor assembly 60. In this embodiment, the fins 49assist in providing a stable flow through the sensor zone 41. Referringto FIG. 18B, the fins 49 may also function as tamper guards orprotection guards to prevent assess by a user to the sensor assembly 60which may contain sensitive or calibrated sensor components. In thisembodiment the fins 49 are integrally formed and suspended down into theinlet zone from the upper lid 36 a of the base compartment 36, althoughit will be appreciated that the fins may alternatively be integrallyformed with or attached so as to extend up into the inlet zone from thebase or underside portion 26 a of the lower housing part 26. It willalso be appreciated that the fins need not necessarily be verticallyoriented, but may alternatively be horizontally oriented such that theyextend from the side walls of the inlet zone of the inlet flow path, ororiented at any other suitable angle or mixtures of angles.

The sensor zone 41 is defined between the end of the inlet zone atapproximately transition line EE to the start of the transition zone 43at approximately transition line FF. The sensor zone comprises a modularremovable sensor assembly 60 of the type previously described withreference to FIGS. 15-17 and which is situated in-line with the bulkflow path for sensing various characteristics or parameters of the gasesstream. As shown, the terminating portion of the side walls 45, 47extend into the front opening side of the sensor assembly 60 and theterminating portions of a loop wall 51 of the transition zone 43 extendsinto the opposite rear exit side of the sensor assembly 60. In a similarmanner to the embodiment described with reference to FIGS. 15-17, thesensor assembly 60 is releasably retained within a retaining gapprovided or formed between the terminating portions of the side walls45, 47 and the loop wall 51.

The transition zone 43 is defined by a substantially curved perimeter orloop wall 51 that may substantially conform to at least a substantialportion of the circumference of a circle, or which is otherwise curvedor concave in shape when viewed in plan. In this embodiment, the loopwall 51 may extend circumferentially about centre point 53. The openinginto the transition zone 43 is defined by the terminating portions ofthe loop wall that extend outwardly relative to the centre point 53 forengaging with exit side of the sensor assembly 60. As shown, thesubstantially circular or bulbous transition zone 43 comprises an outletfor the air flow through exit port 38 provided in the upper lid 36 a ofthe base compartment 36.

As with the spiral inlet flow path embodiment described with referenceto FIGS. 14-17, the shorter direct inlet flow path of FIGS. 18A-18C isalso enclosed from above and below by horizontally extending upper andlower walls or surfaces to form an enclosed channel or air flow passage.The flow path is primarily defined by the co-extending side walls 45,47and loop wall 51, and these side walls are enclosed from above and belowfor example by the upper lid 36 a of the base compartment and the baseor underside portion 26 a of the lower housing part 26 of the mainhousing (see FIG. 7). As shown, in this embodiment the side walls 45,47, 51 are upright and extend substantially perpendicularly orvertically relative to the substantially horizontal enclosing upper lid36 a of the base compartment and underside portion 26 a of the lowerhousing part 26.

Sensor Housing and Location

In the above embodiments, the sensor assembly 60 is located in a sensorzone with the inlet section of the flow path prior to the blower unit.However, the sensor assembly may also be alternatively located in asensor zone situated in any other suitable part of the flow path priorto the humidification unit. In particular, the sensor zone of the flowpath may be located at any location in the flow path upstream of (i.e.,prior to) the humidification unit, including either before or after theblower unit.

The sensor housing and sensors of the sensor assembly 60 will now bedescribed in further detail. The sensor assembly may be employed ineither of the spiral or direct inlet flow path embodiments describedwith reference to FIGS. 14-18C. Referring to FIGS. 19-23, the sensorassembly 60 comprises a sensor housing 62 to which one or more sensorsare mounted for measuring various characteristics of the gases stream inthe bulk flow path. In this embodiment, the sensor housing 62 comprisesa central main body 63 that extends between a first end 74 and secondend 76. The main body 63 is hollow and has openings at both ends suchthat it provides a passageway or sensing passage 86 for the gases streamto pass through from the first end 74 to the second end 76 of the mainbody 63. In particular, the gases stream flows generally in thedirection of the flow axis 110 shown in FIG. 20 that extends from thefirst end 74 to the second end 76 of the main body 63.

In this embodiment, the main body 63 is formed between the first 74 andsecond 76 ends by two spaced-apart vertical side walls 64 and 66, andupper 68 and lower 70 walls that extend horizontally between thevertically extending side walls 64, 66, and where the walls collectivelyform and define the sensing passage. The main body is open at both ends74,76 which in use are aligned with the flow path direction such thatgases stream travels through the hollow interior or cavity of the mainbody defined by the inner surfaces of the side, upper and lower walls.In this embodiment, the width W between the side walls 64, 66 and theheight (H) between the upper and lower walls 68, 70 substantiallycorresponds to the cross-sectional dimensions of the portion or sectionof the flow path immediately surrounding either side of the sensorassembly.

Mounting of Sensors Temperature and Flow Rate Sensors

Referring to FIGS. 19, 20 and 22, this embodiment of the sensor assemblyis provided with mounting apertures 78, 80 for receiving and retaining atemperature sensor 82 and flow rate sensor 84. For example, atemperature sensor mounting aperture 78 is provided in the upper wall 68of the main body of the sensor housing and is configured to receive andretain a temperature sensor. Likewise, a separate flow rate sensormounting aperture 80 is provided in the upper wall 68 of the main body63 of the sensor housing 62 and is shaped or configured to receive andretain a flow rate sensor. The sensors 82, 84 may be held within theirrespective mounting apertures 78, 80 by friction fit, snap fit or anyother coupling or fixing configuration. The temperature sensor may alsooptionally be provided with infra-red radiation shielding components.

Referring to FIG. 20, the temperature sensor 82 and flow rate sensor 84are mounted such that they are suspended down into sensing passage 86from the upper wall 68 of the main body 63. Preferably, the temperaturesensor 82 and flow rate sensor 84 are suspended substantially centrallybetween the ends 74, 76 of the main body. The sensors 82, 84 need notnecessarily be suspended from the upper wall and need not necessarily bevertically oriented. In other embodiments, the sensors 82, 84 may bemounted or secured to any of the upper, lower or side walls of the mainbody 63 of the sensor housing. Further, the orientation of the sensors82, 84 into the sensing passage from their support or mounting wall maybe vertical, horizontal, or any other suitable angle. The sensors 82, 84need not necessarily be centrally located relative to their supportwall, but may be located at any suitable position within the sensingpassage, central or otherwise. The sensors 82, 84 may also extend fromthe same or different support walls.

In this embodiment, the temperature sensor 82 may be a monolithic,digital, IC, temperature transmitter, but any alternative type oftemperature sensor, whether analogue or digital, may be employed. Inthis embodiment, the temperature sensor 82 is a silicon band-gaptemperature transmitter.

In this embodiment, the flow rate sensor 84 comprises a hot-wireanemometer (HWA) flow detector. In one form, the flow rate sensor 84 isa constant-resistance HWA in which the detector comprises a controlledtemperature heated bead thermister located in the sensing passage andfrom which the flow rate can be determined based on the energy (current)required to maintain the bead at a preset temperature. The presettemperature is preferably configured to be set to a level that does notalter the local temperature of the gases stream flowing in the sensingpassage appreciably in the context of O2 measurement. It will beappreciated that in other forms, the flow rate sensor 84 may comprise aconstant-current HWA in which flow rate is determined from the change inresistance of the heated bead. It will be appreciated that any othersuitable form of flow rate sensor or detector may be used if desired.

Ultrasound Gas Composition Sensor System

In this embodiment, the ultrasound gas composition sensor is implementedand configured to sense the relative gas concentrations of a binary gasmixture in the gases stream using binary gas analysis based on anon-invasive cross-flow beam, pulse or wave of ultrasound energy, aswill be explained in further detail later.

The sensor housing comprises transducer mounting assemblies generallyindicated at 90 and 92 for receiving and retaining ultrasonic transducercomponents of the ultrasound gas composition sensor system. In thisembodiment, the transducer mounting assemblies 90, 92 are provided onopposite sides of the main body 63 such that they support or mount apair of transducers on opposite sides of the sensing passage 86. Thetransducers are aligned with, and face each other across, the sensingpassage 86. The transducer mounting assemblies 90, 92 are mounted orfixed to a respective side wall 64, 66 of the main body. Each transducermounting assembly or formation is configured to provide a retainingcavity 90 a, 92 a that is dimensioned and shaped to receive and retain acomplementary dimensioned and shaped transducer component of the gascomposition sensor system. In this embodiment, the receiving cavities 90a, 92 a are substantially cylindrical and are aligned or coaxial withcircular transducer apertures provided through each of the side walls64, 66 of the main body. FIG. 19 shows a transducer aperture 66 a ofside wall 66, and side wall 64 similarly has a corresponding transduceraperture, although it is not visible. It will be appreciated that thetransducer pair could in alternative embodiments be mounted in the upper68 and lower 70 walls of the main body, with the remaining temperatureand flow rate sensors 82,84 being mounted to extend into the sensingpassage from either side wall 64,66.

Referring to FIGS. 23 and 24, in this embodiment each transducermounting assembly 90, 92 has a cylindrical base portion 90 b, 92 b thatis fixed or mounted at one end to a respective outer surface of arespective side wall 64, 66 of the main body 63, and at the other end isprovided with at least one pair of opposed clips or clipping portions orfingers 90 c, 92 c extending from the cylindrical base portion. Thecylindrical base portion in combination with the extending clipscollectively defines the retaining cavity 90 a, 92 a within which thetransducer component is securely received and retained. In thisembodiment, each transducer mounting assembly is provided with acircular array of clips or clipping portions 90 c, 92 c that areinterspaced about the entire circumference of the cylindrical baseportion 90 b, 92 b. In this embodiment, six clipping portions 90 c, 92 cforming three opposed pairs are provided, but it will be appreciatedthat the number of pairs of clipping portions may be varied if desired.

The clipping portions 90 c, 92 c may be resiliently flexible such thatthey may be flexed slightly outwardly relative to their respectivereceiving cavity 90 a, 92 a axis indicated at 90 d, 92 d respectively.The clipping portions 90 c, 92 c may also be configured to taper indirection toward their respective cavity axis 90 d, 92 d as they extendaway from their respective cylindrical base portions 90 b, 92 b. Thisprovides a cylindrical retaining cavity with reducing or graduallytapering diameter as it extends away from the base portion 90 b, 92 b.As shown in FIG. 24, each clipping portion 90 c, 92 c is substantiallyarcuate or concave in shape when viewed in cross-section along itslength extending away from its associated cylindrical base portion 90 b,92 b such that it conforms to a circumferential portion of a cylinder.Referring to FIG. 23, by way of example each clipping portion extendsbetween a first end 94 located at the cylindrical base portion 90 b anda second or terminating end 96 which defines the end of the transducerreceiving cavity 90 a. In this embodiment, the inner surfaces towardterminating end 96 of each clipping portion are provided with a ridge orshoulder portion 97 that extends into the retaining cavity and which isconfigured to act as a stop or grip formation for securing thetransducer component within its retaining cavity.

When installing the transducer components, which are typicallycylindrical in shape, within their respective transducer mountingassemblies 90, 92, the clipping portions 90 c, 92 c flex slightlyoutwardly upon partial insertion of the transducer components and thenrevert to their rest state upon full engagement of the transducerswithin the cavities to thereby securely grip or hold the transducerwithin its respective retaining cavity.

It will be appreciated that other transducer mounting assemblies couldalternatively be used to receive and retain the transducer elementswithin the sensor housing if desired. Preferably, the transducermounting assemblies are configured to allow the transducer components tobe releasably secured, such that the transducers can be removed from thesensor housing for replacement or repair if desired.

In this embodiment, the main body 63 and transducer mounting assembliesare integrally formed with each other from a suitable material, such asplastic. However, it will be appreciated that the parts of the sensorhousing may be formed separately and then fixed or connected together.

Referring to FIG. 20, transducers 100, 102 are shown installed in theirrespective transducer mounting assemblies 90, 92 of the sensor housing.In this embodiment, the transducers and transducer mounting assembliesare configured to cooperate such that the front surfaces of thetransducers extend into their respective transducer apertures in theside walls 64,66 of the main body 63 such that they sit flush with theremaining inner surfaces of the side walls. For example, with referenceto FIG. 20, the front surface 102 b of transducer 102 is shown to besubstantially flush with the inner surface 66 b of the side wall 66. Thesame configuration is provided for the opposing transducer component100.

As shown, this configuration provides a pair of transducers 100,102 thatare aligned and facing each other from opposite sides of the sensingpassage 86 of the main body 63 such that ultrasound waves aretransmitted in a direction that is substantially perpendicular to thedirection or flow axis 110 of the flow of gases travelling through thepassage 86 from the first end 74 to the second end 76 of the main body.

The distance (e.g. indicated by W in FIG. 19) between the pair oftransducers 100,102, which defines the acoustic beam path length, isselected to be large enough to provide the desired sensitivity but shortenough to avoid phase wrap-around ambiguity. For example, the distancebetween the transducers is selected to be large enough to increasesensitivity, but is limited based on the total phase shift expected forthe range of gas compositions and temperatures being sensed.

Sensor Control System and Circuitry

Referring to FIG. 20, the electrical terminals or connectors 100 a, 102a of the transducers 100, 102 protrude out from the sides of the mainbody 63 of the sensor housing and the electrical terminals 82 a, 84 a ofthe temperature and flow rate sensors 82,84 are accessible at the outersurface of the upper wall 68 of the main body 63. A flexible wiring loomor tape 112 may extend across the sides and upper surface of the sensorhousing to provide wiring connections to the electrical terminals of thesensors. The wiring 112 extends to the sensor control system andcircuitry of the respiratory device 10 which is configured to controlthe sensors, as will now be described in further detail.

Referring to FIG. 25, an example of the sensor control system 150 thatis electrically connected via the wiring 112 to the sensor components100,102,84, and 82 will be described by way of example. It will beappreciated that the electronic sensor control system 150 may beimplemented in software or hardware, including implementation on anyprogrammable device such as a microprocessor, microcontroller, DigitalSignal Processor or similar, and which may have memory and associatedinput and output circuitry as will be appreciated. It will beappreciated that the various modules of the sensor control system 150may be varied or separated further or integrated and FIG. 25 will bedescribed by way of example only as to the general functionality of thesensor control system. The sensor control system 150 may be integratedwith the main control system of the respiratory device or may be aseparate sub-system that communicates with the main controller orcontrol system. The sensor control system 150 will be described withreference to a particular arrangement or configuration of sensors thatare arranged for determining the gas composition or relativeconcentrations of gases in a binary gas mixture, such as an air/oxygenmixture, which is substantially equivalent to a nitrogen/oxygen mixture.However, it will be appreciated that the sensor control system may beadapted to provide information indicative of other gas concentrationswithin the gases stream.

Flow Rate Module

The flow rate sensor 84 is configured to sense the flow rate, forexample in Litres per minute, of the gases stream 110 flowing throughthe sensing passage 86 of the sensor housing and generate arepresentative flow rate signal 152 that is received and processed byflow rate module 154 in the sensor control system 150. A motor speedsensor 120 is also preferably provided in the blower unit for sensingthe motor speed, for example in revolutions per minute (rpm) of blowerunit motor. The motor speed sensor 120 generates a representative motorspeed signal 156 that is received and processed by motor speed module158.

Temperature Module

A temperature module 160 is configured to receive and process atemperature signal 162 that is generated by the temperature sensor 82which represents the temperature of the gases stream flowing through thesensing passage 86 of the sensor housing. In this embodiment, thetemperature sensor 82 is configured to sense the temperature of thegases stream in the vicinity of the acoustic beam path between thetransducers 100, 102.

The temperature module 160 is optionally configured to apply temperaturecompensation to the temperature signal 162 to compensate for potentialerrors or offsets generated by the temperature sensor 82. In particular,as the sensor assembly 60 is located below the blower unit compartmentand other electronic circuitry, heat from the circuitry and motor,depending on the operating conditions, can impact on the temperature assensed by the temperature sensor 82. For example, due to the heat abovethe sensor assembly, the temperature signal 162 may indicate a gasstream temperature that is higher than the true temperature. Tocompensate for this potential error when in certain operatingconditions, the temperature module 160 is configured to apply atemperature compensation factor or correction based on the followingformula: Tcorrected=Tsensor+ΔT, where: Tcorrected is the correctedtemperature after compensation, Tsensor is the temperature as sensed bythe temperature sensor 82 as represented by signal 162, and ΔT is thecalculated or predicted temperature error based on the current operatingconditions of the respiratory device.

The temperature error (ΔT) will vary depending on the operatingconditions of the respiratory device 10. In this embodiment, thetemperature error is calculated based on a proportional relationshipwith the system conditions relating to the current flow rate 152 of thegases stream in the respiratory device and the current motor speed 156.Typically, an increased flow rate has a cooling effect while increasedmotor speed causes increased heating within the housing of therespiratory device due to higher power usage. In operation, thetemperature module is configured to continuously or periodicallycalculate the temperature error ΔT based on the current system operatingconditions, and in particular, the current flow rate 152 and motor speed156. The updated temperature error ΔT is then applied to the incomingsensed temperature, Tsensor 162 from the temperature sensor to generatethe corrected temperature, Tcorrected.

In one embodiment, ΔT=α×(motor speed/flow rate), where α is a constant.However, it will be appreciated that ΔT may alternatively be calculatedbased on a look-up table or other algorithm which takes into account oneor more other operating conditions or system variables relating to theoperation of the respiratory device and which have an impact on thetemperature variation that is likely to occur in the vicinity of thetemperature sensor 82. In some embodiments, ΔT may incorporate timedependent effects which have an impact on the temperature variation,such as heat storage in the respiratory device during long run periods.For example, ΔT may also be expressed as an integro-differentialequation to express time variant effects such as those caused by thermalcapacitance of one or more parts of the respiratory device.

Gas Composition Module

The gas composition sensor system is configured as an ultrasound binarygas sensing system. As mentioned, the gas composition sensing system inthis embodiment comprises a pair of ultrasonic transducer components100, 102 that are provided on opposite sides of the sensing passagewayof the sensor housing. One of the transducer components 100 isconfigured as an ultrasonic transmitter for transmitting aunidirectional ultrasound or acoustic beam wave or pulse across thepassageway in a direction substantially perpendicular to the directionof the gases flow stream through the sensing passage to the otherultrasonic transducer which is configured as an ultrasonic receiver toreceive the transmitted ultrasonic wave or pulse on the other side ofthe passage. In this embodiment, the transducer components 100, 102 maybe piezo-ceramic transducer elements, typically operating at a narrowbandwidth, or any other suitable operable ultrasonic transducerelements. In this embodiment, the transducer elements operate at afrequency of approximately 25 kHz, although this may be varied asdesired. In preferred forms, the operating frequency is selected to beabove the human audible acoustic spectrum so that the gas compositionsensing is silent to the user and/or at a high enough frequency toreduce or minimise interference from noise sources.

The ultrasonic transmitter 100 and receiver 102 are controlledrespectively by driver 170 and receiver 172 circuitry of the gascomposition module 174. In particular, the driver circuitry 170 providesa control excitation signal 176 to the ultrasonic transducer to drive itto transmit pulses of ultrasonic energy. The ultrasonic receiver 102senses the pulse and generates a representative reception signal 178that is received and processed by its receiver circuitry 172. While apulsed system is utilized in this embodiment, a continuous wave orstanding wave approach may be employed in alternative embodiments.

Binary gas analysis using ultrasound is based on sensing the speed of anacoustic pulse through the gas sample, which in this case is the bulk orprimary flow of the gases stream flowing through sensing passage 86 ofthe sensor housing. The speed of sound is a function of gas meanmolecular weight and temperature. In this configuration, the gascomposition module 174 receives a temperature signal 164 from thetemperature module 160 representing an indicative temperature of thegases flowing between the beam path between ultrasonic transducers. Withknowledge of sensed speed of sound and sensed temperature, the gascomposition in the gases stream may be determined or calculated. Inparticular, measurements of the speed of sound across the sensingpassage may be used to infer the ratios of two known gases by referenceto empirical relationships, standard algorithms, or data stored in theform of look-up tables, as is known in the art of binary gas analysiswith ultrasound. It will be appreciated that alternatively an estimateof the temperature of the gases stream in the beam path of theultrasound transducers may be used in the binary gas analysiscalculations if a temperature sensor is not employed. In suchalternative embodiments, the temperature of the gases stream may beconditioned or controlled to within a narrow temperature band to enablean estimate of temperature of the gases stream in the beam path to beused.

In some embodiments, the respiratory device may also be provided with ahumidity sensor that is located in the flow path and which is configuredto generate a humidity signal indicative of the humidity of the gasesstream flowing through the sensor assembly. In such embodiments, the gascomposition may be determined by the sensed speed of sound, and thesensed temperature and/or sensed humidity. The humidity sensor may be arelative humidity sensor or an absolute humidity sensor. In someembodiments, the gas composition may be determined based on the sensedspeed of sound and the sensed humidity, without the need for atemperature sensor.

The gas composition sensing system may be used to measure respectiveratios of any two known gases in a gas composition. In this embodiment,the gas composition module is configured to determine the relative gasconcentration in a mixture of air blended with supplementary oxygen,which is substantially equivalent to a nitrogen/oxygen mixture. In sucha binary gas mixture, by monitoring the speed of sound and taking thetemperature into account, the mean molecular weight of the gas can bedetermined, and thus, the relative concentrations of the two gases maybe determined. From this ratio, the oxygen fraction or nitrogen fractionof the gases stream may be extracted.

In this embodiment, the gas composition module 124 comprises an analyseror controller 180 that is configured to operate the ultrasonictransducers 100, 102 via their respective driver 170 and receiver 172circuitry with control signals 171, 173. The analyser 180 is alsoconfigured to receive and process the corrected temperature signal 164from the temperature module 160. In operation, the analyser 180 isconfigured to periodically at a desired frequency transmitunidirectional ultrasonic or acoustic pulses across the sensing passageto determine the speed of sound of the acoustic pulses. The measure ofspeed of sound is then used to determine the gas composition withknowledge of the temperature from the temperature module 160. The speedof the acoustic pulse may be determined in any desired manner, includingusing timer circuitry to determine the transit time of the acousticpulse to travel across the passageway from the transmitter 100 to thereceiver 102 either directly or indirectly via phase detection. It willbe appreciated that phase can be tracked to minimise ‘wrap-around’effects if suitable signal processing is implemented. The distancebetween the transducer elements 100, 102 is known and equivalent to thewidth (W in FIG. 19) between the side walls 64, 66 of the sensor housingand therefore the speed of sound can be determined based on the transittime and distance between the transducers (which corresponds to the beampath length). In particular, the analyser may be pre-programmed andcalibrated with the data indicative of the distance between thetransducers, and/or any other generally applicable or device specificcharacteristics useful in determining gas composition via speed of soundsensing. The calibration can take into account the change in distancebetween the transducer elements 100, 102 as a function of thetemperature. For example, the distance between the side walls 64, 66 ofthe sensor housing may increase or decrease as the temperature changes.

Optionally, the gas composition sensor module may be configured with auser selectable or pre-programmed scale factor or correction factor toaccount for argon when determining the oxygen fraction, which ispreferably used when oxygen is supplied to the respiratory device from acommercial oxygen concentrator that uses a pressure swing adsorptiontechnique. For example, the user may activate the control system toemploy the argon scale or correction factor to modify the sensed oxygenfraction to remove any argon component to yield the computed oxygenfraction.

The sensor control system 150 may output data or signals indicative ofthe various characteristics sensed by the sensor assembly or othersensors. For example, output signals or data 182, 184, and 186 frommodules 154, 158, 160 may represent the sensed flow rate 182, motorspeed 184, and temperature 186. Likewise, the gas composition module isconfigured to generate one or more output signals or data 188 indicativeof the gas composition as sensed by the ultrasound gas compositionssensing system. In this embodiment, the output signal 188 may representthe oxygen fraction or oxygen (O2) concentration in the gases stream.Alternatively, the signal or an additional signal may represent nitrogen(N2) concentration or fraction. It will also be appreciated that thesystem may be modified to provide signals representing other gasconcentrations within the gases stream, including, but not limited to,carbon dioxide (CO2) for example.

The gas concentration output signal or signals 188 may then be receivedand processed by the main controller of the respiratory device. Forexample, the main controller may be configured to display a sensedoxygen reading on an output display of the respiratory device based onthe oxygen signal 188. In one embodiment, the user control interface 30(see FIG. 8) may be configured to display a gas concentration reading,e.g. oxygen concentration or other one or more gas concentration levels,as sensed by the ultrasound gas composition sensor system.

In some embodiments, the main controller is configured to determinewhether one or more gas concentration levels, for example the oxygenconcentration, stays within user-defined ranges, defined by maximumand/or minimum thresholds. For example, in such embodiments, the maincontroller may be configured to compare the sensed gas concentrationlevel based on the gas concentration output signal 188 to theuser-defined or selected gas concentration level thresholds. If thesensed level is below the minimum threshold, or above a maximumthreshold, or otherwise outside a user-defined range, the maincontroller may trigger or activate an alarm incorporated into thedevice, which may be audible, visual, tactile, or any combination ofthese. The main controller may optionally also shut-down the device ortrigger any other appropriate operational functions appropriate to therespective, triggered alarm.

In some embodiments, the respiratory device 10 comprises a disinfectionsystem and/or cleaning mode of the type described in WO 2007/069922, thecontents of which are incorporated by reference. Such disinfectionsystems employ thermal disinfection by circulating heated dry gasesthrough portions of the gases flow path to the user interface. In suchembodiments, the main controller is configured to determine whether theoxygen concentration level in gases flow path is below a preset oxygenconcentration level based on the sensed oxygen signal 188 prior tocommencing any disinfection system or cleaning mode. For example, themain controller may be configured to prevent initiation of any cleaningmode until the sensed oxygen fraction is within a safe range, preferablybelow about 30%, to minimize fire hazards.

The oxygen signal 188 may additionally be used to automatically controlthe motor speed of the blower unit to alter the flow rate of the gasesstream to thereby alter or modify the oxygen fraction to the desiredlevel, or to halt operation of the device should the oxygen fractionmove outside preset upper or lower thresholds. Alternatively, the userof the respiratory device may manually control the flow rate of theoxygen supply from the central gases source connected to the respiratorydevice to thereby vary the oxygen fraction based on real-time feedbackfrom the displayed oxygen reading, without needing to estimate theoxygen fraction based on printed look-up tables. In some embodiments,the respiratory device may have a valve that automatically alters ormodifies the flow rate of the oxygen supply from the central gasessource to thereby vary the oxygen fraction. The main controller canreceive the oxygen signal 188 and adjust the oxygen valve accordinglyuntil a predetermined value for the oxygen signal 188 is reached, whichcorresponds to a desired oxygen fraction.

Alternative Ultrasound Gas Composition Sensor System Configurations

Referring to FIGS. 26A-26E, various alternative configurations of theultrasonic transducers will be described for the gas composition sensingsystem for sensing the speed of sound through the gases stream by thetransmission and reception of cross-flow ultrasonic beams or pulses.Like reference numerals, represent like components.

Referring to FIG. 26A, the transducer configuration 200 of theembodiment described above with reference to FIGS. 19-25 isschematically illustrated. As shown, the transducer configurationprovides an arrangement in which there is a pair of transducers 202,204opposing each from opposite sides of the sensing passage 206, with theair flow path direction indicated generally by 208. In thisconfiguration 200, each of the transducers 202,204 is driven as either adedicated transmitter or receiver, such that ultrasonic pulses 210 aretransmitted uni-directionally across the air flow path from thetransmitter to the receiver transducer. As shown, the transducer pair isaligned (i.e. not-displaced upstream or downstream from each other)relative to the air flow path direction 208 and is configured totransmit cross-flow pulses that are substantially perpendicular to theair flow path direction.

Referring to FIG. 26B, an alternative transducer configuration 220 isillustrated in which a pair of transducers 222,224 is provided opposingeach other on opposite sides of the sensing passage, but wherein eachtransducer may operate as both a transmitter and receiver, i.e. is anultrasonic transmitter-receiver or transceiver. In this configuration,bi-directional ultrasonic pulses 226 may be sent between the transducerpair 222,224. For example, pulses may be sent back and forth alternatelybetween the transducers or in any other sequence or pattern. Again, thetransducer pair is aligned relative to the air flow path direction andare configured to transmit cross-flow pulses that are substantiallyperpendicular to the air flow path direction.

Referring to FIG. 26C, an alternative echo transducer configuration 230is illustrated in which the transmitter and receiver transducer pair isprovided in the form of a single ultrasonic transmitter-receivertransducer 232 that is provided on one side of the sensing passage andwhich is configured to transmit cross-flow acoustic pulses 236 acrossthe sensing passage 206 and receive the reflected pulse or echoreflected back from the opposite side of the sensing passage.

Referring to FIG. 26D, an alternative transducer configuration 240 isillustrated in which the transmitter transducer 242 and transmitterreceiver 244 are displaced from one another relative to the air flowpath direction (i.e. one is upstream from the other) and on oppositesides of the sensing passage. In FIG. 26D, the receiver is upstream fromthe transmitter, although an opposite configuration could be employed.With this arrangement, the transmitter 242 may either transmit directcross-flow pulses across the sensing passage 206 to the receiver 244 asshown by beam 246, or may create a longer indirect path length by areflected path comprising at least two reflections as indicated by beam248. As shown, with this displaced configuration, the acoustic pulseshave a cross-flow direction that is angularly traversing rather thansubstantially perpendicular to air flow path direction 208. It will alsobe appreciated that while a uni-directional configuration is shown, thetransducers 242,244 may alternatively be ultrasonictransmitter-receivers to enable bi-directional beam pulses to betransmitted back and forth between the transducers (i.e. both upstreamand downstream relative to the air flow).

Referring to FIG. 26E, an alternative transducer configuration 250 isillustrated that is a modification of the configuration of FIG. 26Dwhere the transmitter 252 and receiver 254 are again displaced from eachother in the air flow direction 208 but where they are located on thesame side of the sensing passage such that the transmitted cross-flowpulses 256 comprise at least one reflection (or multiple reflections fora longer path length) from the opposing side of the sensing passage 206.Otherwise, the same alternative options as that described with referenceto FIG. 26D apply, including bi-directional operation and switching thelocation of the transmitter and receiver.

Referring to FIGS. 27A-27C, various further alternative configurationsof the ultrasonic transducers will be described for the gas compositionsensing system for sensing the speed of sound through the gases streamby the transmission and reception of along-flow ultrasonic beams orpulses. Like reference numerals represent like components.

Referring to FIG. 27A, an alternative transducer configuration 260 isillustrated in which there is a pair of transducers 262,264 opposingeach other from opposite ends of the sensing passage 206, with the airflow path direction or axis indicated generally by 208. In thisconfiguration 260, each of the transducers 262,264 is driven as either adedicated transmitter or receiver, such that along-flow ultrasonicpulses 266 are transmitted uni-directionally in a beam path between thetransmitter and receiver that is substantially aligned or parallel withthe gases flow path axis 208 in the sensing passage 206. In theembodiment shown, the transmitter is upstream of the receiver, but itwill be appreciated that the opposite arrangement could be employed.With this configuration, a flow rate sensor is provided in the sensingpassage to provide a flow rate signal indicative of the flow rate of thegases stream in the sensing passage. It will be appreciated that thespeed of sound in the sensing passage can be derived or determined in asimilar manner to that previously described with the previousembodiments, and that the flow rate signal is utilized in the signalprocessing to remove or compensate for the gases flow rate in thecalculated speed of sound signal.

Referring to FIG. 27B, an alternative transducer configuration 270 isillustrated in which a pair of transducers 272,274 is provided opposingeach other from opposite ends of the sensing passage like in FIG. 27A,but wherein each transducer may operate as both a transmitter andreceiver, i.e. is an ultrasonic transmitter-receiver or transceiver. Inthis configuration, bi-directional along-flow ultrasonic pulses 276 maybe sent between the transducer pair 272,274. For example, pulses may besent back and forth alternately between the transducers or in any othersequence or pattern. Again, the transducer pair are aligned with the airflow path axis 208 and are configured to transmit cross-flow pulses in abeam path or paths that are substantially aligned or parallel to the airflow path axis 208 in the sensing passage 206. With this configuration,a separate flow rate sensor need not necessarily be provided, as theflow rate component of the speed of sound signal can be directly derivedor determined from processing of the transmitted and received acousticpulses.

Referring to FIG. 27C, an alternative echo transducer configuration 280is illustrated in which the transmitter and receiver transducer pair isprovided in the form of a single ultrasonic transmitter-receivertransducer 282 that is provided at one end of the sensing passage(whether at the start or end) and which is configured to transmitalong-flow acoustic pulses 286 along the sensing passage 206 in a beampath substantially aligned or parallel to the air flow axis 208 andreceive the reflected pulse or echo reflected back from the opposite endof the sensing passage. In the embodiment shown, thetransmitter-receiver 282 is shown at the end of the passage, but itcould alternatively be located at the start of the passage. Like theconfiguration of FIG. 27A, a flow rate sensor is provided in the sensingpassage to enable the speed of sound calculation to compensate for theair flow rate component.

With the alternative configurations of FIGS. 26B-26E and 27A-27C, itwill be appreciated that the driver and receiver circuitry, and signalprocessing, can be adapted accordingly for the sensing of the speed ofsound in the sensing passage, which is then in turn used to determinethe gas composition as previously explained.

Preferred Features:

1. A respiratory assistance apparatus configured to provide a heated andhumidified gases stream, comprising: a gases inlet configured to receivea supply of gases; a blower unit configured to generate a pressurisedgases stream from the supply of gases; a humidification unit configuredto heat and humidify the pressurised gases stream; a gases outlet forthe heated and humidified gases stream; a flow path for the gases streamthrough the respiratory device from the gases inlet through the blowerunit and humidification unit to the gases outlet; a sensor assemblyprovided in the flow path before the humidification unit, the sensorassembly comprising an ultrasound gas composition sensor system forsensing one or more gas concentrations within the gases stream.

2. A respiratory assistance apparatus according to paragraph 1 whereinthe ultrasound gas composition sensor system comprises a transmitter andreceiver transducer pair that are operable to transmit cross-flowacoustic pulses from the transmitter to the receiver through the gasesstream for sensing the speed of sound in the gases stream in thevicinity of the sensor assembly.

3. A respiratory assistance apparatus according to paragraph 2 whereinthe transmitter and receiver transducer pair are arranged such that theacoustic pulses traverse the gases stream in a direction substantiallyperpendicular to the flow direction of the gases stream.

4. A respiratory assistance apparatus according to paragraph 2 whereinthe transmitter and receiver transducer pair are arranged such that theacoustic pulses traverse the gases stream in a cross-flow that is angledbut not perpendicular with respect to the flow direction of the gasesstream.

5. A respiratory assistance apparatus according to any one of paragraphs2-4 wherein the transmitter and receiver transducer pair comprises atransducer that is configured as a transmitter and a transducer that isconfigured as a receiver for transmitting uni-directional acousticpulses.

6. A respiratory assistance apparatus according to any one of paragraphs2-4 wherein the transmitter and receiver transducer pair comprises apair of transmitter-receiver transducers that are configured fortransmitting bi-directional acoustic pulses.

7. A respiratory assistance apparatus according to paragraph 5 orparagraph 6 wherein the transmitter and receiver are aligned with eachother in relation to the flow direction of the gases stream and facingeach other on opposite sides of the flow path.

8. A respiratory assistance apparatus according to paragraph 5 orparagraph 6 wherein the transmitter and receiver are displaced from eachother in the flow direction of the gases stream.

9. A respiratory assistance apparatus according to paragraph 8 whereinthe acoustic pulses have a beam path that is direct between thetransmitter and receiver.

10. A respiratory assistance apparatus according to paragraph 8 whereinthe acoustic pulses have a beam path that is indirect between thetransmitter and receiver and which undergoes one or more reflections.

11. A respiratory assistance apparatus according to any one ofparagraphs 2-4 wherein the transmitter and receiver transducer pair isin the form of a single transmitter-receiver that is configured totransmit cross-flow acoustic pulses and receive the echo return pulses.

12. A respiratory assistance apparatus according to paragraph 2 whereinthe ultrasound gas composition sensor system comprises a transmitter andreceiver transducer pair that are operable to transmit along-flowacoustic pulses from the transmitter to the receiver through the gasesstream for sensing the speed of sound in the gases stream in thevicinity of the sensor assembly.

13. A respiratory assistance apparatus according to any one ofparagraphs 2-12 further comprising a sensor control system that isoperatively connected to the transmitter and receiver transducer pair ofthe ultrasound gas composition sensor system and which is configured tooperate the transducer pair to sense and generate a speed of soundsignal indicative of the speed of sound through the gases stream.

14. A respiratory assistance apparatus according to paragraph 13 whereinthe sensor control system is configured to generate one or more gasconcentration signals indicative of the gas concentration within thegases stream based at least on the signal indicative of the speed ofsound though the gases stream.

15. A respiratory assistance apparatus according to paragraph 13 orparagraph 14 wherein the sensor assembly further comprises a temperaturesensor that is configured to measure the temperature of the gases streamin the vicinity of the sensor assembly and generate a representativetemperature signal, and wherein the sensor control system is configuredto generate one or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of sound signaland the temperature signal.

16. A respiratory assistance apparatus according to paragraph 13 orparagraph 14 wherein the sensor assembly further comprises a humiditysensor that is configured to measure the humidity in the gases stream inthe vicinity of the sensor assembly and generate a representativehumidity signal, and wherein the sensor control system is configured togenerate one or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of sound signaland the humidity signal.

17. A respiratory assistance apparatus according to paragraph 13 orparagraph 14 wherein the sensor assembly further comprises a temperaturesensor that is configured to measure the temperature of the gases streamin the vicinity of the sensor assembly and generate a representativetemperature signal and a humidity sensor that is configured to measurethe humidity in the gases stream in the vicinity of the sensor assemblyand generate a representative humidity signal, and wherein the sensorcontrol system is configured to generate one or more gas concentrationsignals indicative of the gas concentration within the gases streambased on the speed of sound signal, temperature signal, and humiditysignal.

18. A respiratory assistance apparatus according to paragraph 15 orparagraph 17 wherein the sensor control system is configured to apply atemperature correction to the temperature signal to compensate for anypredicted temperature sensing error created by heat within therespiratory device that affects the temperature sensor.

19. A respiratory assistance apparatus according to paragraph 18 whereinthe sensor assembly further comprises a flow rate sensor that isconfigured to sense the flow rate of the gases stream in the vicinity ofthe sensor assembly and generate a representative flow rate signal; andthe system further comprises: a motor speed sensor being provided thatis configured to sense the motor speed of the blower unit and generate arepresentative motor speed signal, and wherein the temperaturecorrection is calculated by the sensor control system based at least onthe flow rate signal and/or motor speed signal.

20. A respiratory assistance apparatus according to any one ofparagraphs 13-19 wherein the sensor control system is configured togenerate a gas concentration signal representing the oxygenconcentration in the gases stream.

21. A respiratory assistance apparatus according to any one ofparagraphs 13-19 wherein the sensor control system is configured togenerate a gas concentration signal representing the carbon dioxideconcentration in the gases stream.

22. A respiratory assistance apparatus according to any one ofparagraphs 1-21 wherein the sensor assembly is releasably mounted withinthe flow path.

23. A respiratory assistance apparatus according to any one ofparagraphs 1-22 wherein the flow path is shaped or configured to promotestable flow of the gases stream in at least one section or portion ofthe flow path.

24. A respiratory assistance apparatus according to paragraph 23 whereinthe flow path is shaped or configured to promote stable flow in asection or portion of the flow path containing the sensor assembly.

25. A respiratory assistance apparatus according to paragraph 23 orparagraph 24 wherein the flow path comprises one or more flow directorsat or toward the gases inlet.

26. A respiratory assistance apparatus according to paragraph 25 whereineach flow director is in the form of an arcuate fin.

27. A respiratory assistance apparatus according to any one ofparagraphs 23-26 wherein the flow path comprises at least one spiralportion or section to promote stable flow of the gases stream.

28. A respirator assistance apparatus according to paragraph 27 whereinthe flow path comprises an inlet section that extends between the gasesinlet and the blower unit and the inlet section comprises at least onespiral portion.

29. A respiratory assistance apparatus according to paragraph 27 orparagraph 28 wherein the sensor assembly is located in a spiral portionof the flow path.

30. A respiratory assistance apparatus according to paragraph 29 whereinthe spiral portion comprises one or more substantially straightsections, and the sensor assembly is located in one of the straightsections.

31. A respiratory assistance apparatus according to any one ofparagraphs 2-30 wherein the sensor assembly comprises a sensor housingcomprising a main body that is hollow and defined by peripheral wallsthat extend between a first open end and a second open end to therebydefine a sensing passage in the main body between the walls throughwhich the gases stream may flow in the direction of a flow axisextending between the first and second ends of the main body and whereinthe transmitter and receiver transducer pair are located on oppositewalls or sides of the sensing passage.

32. A respiratory apparatus according to paragraph 31 wherein the sensorhousing comprises: a main body comprising two spaced-apart side walls,upper and lower walls extending between the side walls to define thesensing passage along the main body between its first and second ends;and a pair of transducer mounting assemblies located on opposing wallsof the main body, which are each configured to receive and retain arespective transducer of the transducer pair such that they are aligned,and face each other, across the sensing passage of the main body.

33. A respiratory assistance apparatus according to any one ofparagraphs 1-32 wherein the blower unit is operable to generate a gasesstream at the gases outlet having a flow rate of up to 100litres-per-minute.

34. A respiratory assistance apparatus according to any one ofparagraphs 1-33 wherein the gases inlet is configured to receive asupply of gases comprising a mixture of atmospheric air and pure oxygenfrom an oxygen supply.

35. A respiratory assistance apparatus according to any one ofparagraphs 1-33 wherein the gases inlet is configured to receive asupply of gases comprising a mixture of atmospheric air and carbondioxide from a carbon dioxide supply.

36. A respiratory assistance apparatus according to any one ofparagraphs 1-35 wherein the flow path is in the bulk flow path of theapparatus.

37. A sensor assembly for in-line flow path sensing of a gases stream ina respiratory assistance apparatus comprising: a sensor housingcomprising a main body that is hollow and defined by peripheral wallsthat extend between a first open end and a second open end, to therebydefine a sensing passage in the main body between the walls, throughwhich the gases stream may flow in the direction of a flow axisextending between the first and second ends of the main body; anultrasound gas composition sensor system mounted in the sensor housingfor sensing one or more gas concentrations within the gases streamflowing in the sensing passage; a temperature sensor mounted in thesensor housing for sensing the temperature of the gases stream flowingin the sensing passage; and a flow rate sensor mounted in the sensorhousing for sensing the flow rate of the gases stream flowing in thesending passage.

38. A sensor assembly according to paragraph 37 wherein the sensorhousing is configured for releasable engagement into a complementaryretaining aperture in the flow path of the respiratory assistanceapparatus.

39. A sensor assembly according to paragraph 37 or paragraph 38 whereinthe ultrasound gas composition sensor system comprises a transmitter andreceiver transducer pair that are operable to transmit acoustic pulsesfrom the transmitter to the receiver through the gases stream in adirection substantially perpendicular to the flow axis of the gasesstream flowing through the sensing passage.

40. A sensor assembly according to paragraph 39 wherein the transmitterand receiver transducer pair are located on opposite walls or sides ofthe sensing passage.

41. A sensor assembly according to paragraph 39 or paragraph 40 whereinthe main body of the sensor housing comprises two spaced-apart sidewalls, and upper and lower walls that extend between the side walls todefine the sensing passage along the main body between its first andsecond ends; and a pair of transducer mounting assemblies located onopposing walls of the main body, which are each configured to receiveand retain a respective transducer of the transducer pair such that theyare aligned, and face each other, across the sensing passage of the mainbody.

42. A sensor assembly according to paragraph 41 wherein the pair oftransducer mounting assemblies are located on opposite side walls of themain body, and wherein each transducer mounting assembly comprises aretaining cavity within which a respective transducer of the pair arereceived and retained.

43. A sensor assembly according to paragraph 42 wherein each transducermounting assembly comprises a cylindrical base portion that extends froma respective side wall of the main body and at least one pair of opposedclips that extend from the base portion, the base portion and clipscollectively defining the retaining cavity.

44. A sensor assembly according to paragraph 43 wherein each side wallof the main body comprises a transducer aperture which is co-alignedwith its associated transducer mounting assembly and through which thefront operating face of the transducer may extend to access the sensingpassage.

45. A sensor assembly according to paragraph 44 wherein the transducermounting assemblies are configured to locate their respectivetransducers such that the operating faces of the transducers aresubstantially flush with the inner surface of their respective wall ofthe main body of the sensor housing.

The foregoing description of the invention includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention as defined by the accompanying claims.

1. A respiratory assistance apparatus configured to provide a heated andhumidified gases stream, comprising: a gases inlet configured to receivea supply of gases; a blower unit configured to generate a pressurisedgases stream from the supply of gases; a humidification unit configuredto heat and humidify the pressurised gases stream; a gases outlet forthe heated and humidified gases stream; a flow path for the gases streamthrough the respiratory device from the gases inlet through the blowerunit and humidification unit to the gases outlet; a sensor assemblyprovided in the flow path before the humidification unit, the sensorassembly comprising an ultrasound gas composition sensor system forsensing one or more gas concentrations within the gases stream.
 2. Arespiratory assistance apparatus according to claim 1 wherein theultrasound gas composition sensor system comprises a transmitter andreceiver transducer pair that are operable to transmit cross-flowacoustic pulses from the transmitter to the receiver through the gasesstream for sensing the speed of sound in the gases stream in thevicinity of the sensor assembly.
 3. A respiratory assistance apparatusaccording to claim 2 wherein the transmitter and receiver transducerpair are arranged such that the acoustic pulses traverse the gasesstream in a direction substantially perpendicular to the flow directionof the gases stream.
 4. A respiratory assistance apparatus according toclaim 2 wherein the transmitter and receiver transducer pair arearranged such that the acoustic pulses traverse the gases stream in across-flow that is angled but not perpendicular with respect to the flowdirection of the gases stream.
 5. A respiratory assistance apparatusaccording to claim 2 wherein the transmitter and receiver transducerpair comprises a transducer that is configured as a transmitter and atransducer that is configured as a receiver for transmittinguni-directional acoustic pulses.
 6. A respiratory assistance apparatusaccording to claim 2 wherein the transmitter and receiver transducerpair comprises a pair of transmitter-receiver transducers that areconfigured for transmitting bi-directional acoustic pulses.
 7. Arespiratory assistance apparatus according to claim 5 wherein thetransmitter and receiver are aligned with each other in relation to theflow direction of the gases stream and facing each other on oppositesides of the flow path.
 8. A respiratory assistance apparatus accordingto claim 5 wherein the transmitter and receiver are displaced from eachother in the flow direction of the gases stream.
 9. A respiratoryassistance apparatus according to claim 8 wherein the acoustic pulseshave a beam path that is direct between the transmitter and receiver.10. A respiratory assistance apparatus according to claim 8 wherein theacoustic pulses have a beam path that is indirect between thetransmitter and receiver and which undergoes one or more reflections.11. A respiratory assistance apparatus according to claim 2 wherein thetransmitter and receiver transducer pair is in the form of a singletransmitter-receiver that is configured to transmit cross-flow acousticpulses and receive the echo return pulses.
 12. A respiratory assistanceapparatus according to claim 2 wherein the ultrasound gas compositionsensor system comprises a transmitter and receiver transducer pair thatare operable to transmit along-flow acoustic pulses from the transmitterto the receiver through the gases stream for sensing the speed of soundin the gases stream in the vicinity of the sensor assembly.
 13. Arespiratory assistance apparatus according to claim 2 further comprisinga sensor control system that is operatively connected to the transmitterand receiver transducer pair of the ultrasound gas composition sensorsystem and which is configured to operate the transducer pair to senseand generate a speed of sound signal indicative of the speed of soundthrough the gases stream.
 14. A respiratory assistance apparatusaccording to claim 13 wherein the sensor control system is configured togenerate one or more gas concentration signals indicative of the gasconcentration within the gases stream based at least on the signalindicative of the speed of sound though the gases stream.
 15. Arespiratory assistance apparatus according to claim 13 wherein thesensor assembly further comprises a temperature sensor that isconfigured to measure the temperature of the gases stream in thevicinity of the sensor assembly and generate a representativetemperature signal, and wherein the sensor control system is configuredto generate one or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of sound signaland the temperature signal.
 16. A respiratory assistance apparatusaccording to claim 13 wherein the sensor assembly further comprises ahumidity sensor that is configured to measure the humidity in the gasesstream in the vicinity of the sensor assembly and generate arepresentative humidity signal, and wherein the sensor control system isconfigured to generate one or more gas concentration signals indicativeof the gas concentration within the gases stream based on the speed ofsound signal and the humidity signal.
 17. A respiratory assistanceapparatus according to claim 13 wherein the sensor assembly furthercomprises a temperature sensor that is configured to measure thetemperature of the gases stream in the vicinity of the sensor assemblyand generate a representative temperature signal and a humidity sensorthat is configured to measure the humidity in the gases stream in thevicinity of the sensor assembly and generate a representative humiditysignal, and wherein the sensor control system is configured to generateone or more gas concentration signals indicative of the gasconcentration within the gases stream based on the speed of soundsignal, temperature signal, and humidity signal.
 18. A respiratoryassistance apparatus according to claim 14 wherein the sensor controlsystem is configured to generate a gas concentration signal representingthe oxygen concentration in the gases stream.
 19. A respiratoryassistance apparatus according to claim 14 wherein the sensor controlsystem is configured to generate a gas concentration signal representingthe carbon dioxide concentration in the gases stream.
 20. A respiratoryassistance apparatus according to claim 2 wherein the sensor assemblycomprises a sensor housing comprising a main body that is hollow anddefined by peripheral walls that extend between a first open end and asecond open end to thereby define a sensing passage in the main bodybetween the walls through which the gases stream may flow in thedirection of a flow axis extending between the first and second ends ofthe main body and wherein the transmitter and receiver transducer pairare located on opposite walls or sides of the sensing passage.
 21. Arespiratory apparatus according to claim 20 wherein the sensor housingcomprises: a main body comprising two spaced-apart side walls, upper andlower walls extending between the side walls to define the sensingpassage along the main body between its first and second ends; and apair of transducer mounting assemblies located on opposing walls of themain body, which are each configured to receive and retain a respectivetransducer of the transducer pair such that they are aligned, and faceeach other, across the sensing passage of the main body.
 22. Arespiratory assistance apparatus according to claim 6 wherein thetransmitter and receiver are aligned with each other in relation to theflow direction of the gases stream and facing each other on oppositesides of the flow path.
 23. A respiratory assistance apparatus accordingto claim 6 wherein the transmitter and receiver are aligned with eachother in relation to the flow direction of the gases stream and facingeach other on opposite sides of the flow path.
 24. A respiratoryassistance apparatus according to claim 23 wherein the acoustic pulseshave a beam path that is direct between the transmitter and receiver.25. A respiratory assistance apparatus according to claim 23 wherein theacoustic pulses have a beam path that is indirect between thetransmitter and receiver and which undergoes one or more reflections.